The use of hydrogel-based wound dressings for the promotion of wound healing is accepted clinical practice for wounds that have low to medium exudate. These dressings are typically applied to the skin as an adhesive bandage. Hydrogel-based wound dressings are cross-linked polymer gels in sheet form, having a gauze or an impervious polymer backing with an adhesive component provided for skin adhesion. Examples include, hydropolymer dressings impregnated with petroleum gauze or having water-resistant permeable polyurethane backing, paste dressings containing zinc oxide and calamine, waterproof foam dressing made of polyurethane film, guaze-based stretchable dressing, alginate-based dressings, collagen-based dressings and silver dressings. Hydrogel sheets are available from several commercial sources, including Tegagel (3M), Vigilon (Bard), Clearsite (Conned Corporation), AQUASORB (DeRoyal), FLEXDERM (Bertek), NU-GEL (Johnson & Johnson), and CURAGEL (Kendall). These adhesive gauze or patch products, however, remain intact and have the disadvantage of being difficult to remove when peeling off from the skin.
Hydrogels have also been employed to increase ocular residence time and enhance bioavailability for drugs applied to the eye. The hydrogels were found to provide better tolerability and less blurring of vision than ointments. Hydrogels used for ocular application are either pre-formed gels or are formed in situ. The pre-formed gels comprise, for example, cellulose derivatives, such as hydroxyethyl cellulose, hydroxymethyl cellulose, carboxymethyl cellulose; polyacrylic acids; cross-linked acrylic acid derivatives (carbomer); polyarcylamides; carbophil; gelatin; hyaluronic acid; polyvinyl alcohol; polyvinyl pyrrolidone; or xanthan gum.
The in situ-forming gels typically comprise cellulose acetate phthalate, polaxomers, ethylene diamine derivative of polaxamine; psuedolatexes prepared by the incorporation of pilocarpine in cellulose acetate phthalate; various copolymers, such as PEO-PLLA and PEG-PLGA-PEG; cellulose acetophalate latex; Gelrite; carbopol; Matrigel; polyethylene oxide, polyoxypropylene, or gellan gum. However, most require a high (>20%) polymer concentration for in situ gel formation. Thermally gelling polymers (Poloxamer, Pluronics, PEO-PLLA diblock copolymer, PEG-PLGA-PEG triblock copolymer, and Matrigel) have a disadvantage of gelling before administration due to temperature change during packaging or storage, and can require manipulation of the temperature before administration. Furthermore, many of these polymers (e.g., Poloxamer and Pluronics) form a hydrogel which is a viscous, but still flowing solution and therefore are not readily applicable for use at a particular site on body surfaces.
An in situ gelling polyvinyl alcohol (PVA)-based, fast cross-linking hydrogel system in the form of a spray, and suitable as a wound dressing, has been disclosed by Bohl Masters, et al., Wound Repair and Regeneration 10 (5), 286-294, 2002; and Bourke, et al., AAPS PharmSci 2003; 5(4) article 33. The PVA is functionalized by reacting with the acrylamide derivatives and are cross-linked by UV irradiation. The hydrogel provides a protective barrier on the skin but the cross-linking is irreversible. Accordingly, these hydrogel systems are not readily soluble and have to be peeled off to be removed them from the site.